This invention relates to a method for filling a contact hole, and more particularly to a method for filling a contact hole with a metal such as selective CVD-tungsten (W).
In the past, in case where an electrode is formed on an inner side surface of a contact hole which is formed in an insulation layer, a metal such as aluminum (Al) etc. is used as material for the electrode and, sputtering method is used for deposition of the metal on inner side surface of the contact hole. However, where the diameter of the contact hole becomes less than one (1) .mu.m, i.e., submicron, it becomes impossible to coat aluminum on the inner side surface of the contact hole by use of a sputtering technique. As a result, aluminum wiring is broken or reliability as to electromigration resistance etc. decreases.
To prevent the occurrence of such problems, a certain technology was proposed (see, Journal of Electrochemical Society, SOLID-STATE SCIENCE AND TECHNOLOGY, "Selective LPCVD Tungsten for Contact Barrier Applications" Levy et al., September 1986, Vol. 133, No. 9, pages 1905-1912, and "Structure of Selective Low Pressure Chemically Vapor-Deposited Films of Tungsten" Green et al., May 1985, Vol. 132, No. 5). The technology relates to selectively filling contact holes with LPCVD tungsten. In this technology, an oxide film is formed on a silicon substrate as a semiconductor substrate, and a contact hole is formed in the oxide film. Then, tungsten (W) as metal is selectively grown in the contact hole.
This technology has, however, some drawbacks. That is, it may occur that tungsten encroaches up to a diffusion layer or in the vertical direction through the diffusion layer due to stress of the oxide film at periphery of bottom surface portion of contact hole so that the junction of the diffusion layer and semiconductor substrate may be broken down.
Further, it may also that tungsten is also deposited on the surface of the oxide film so that tungsten is grown thereon. As a result, it becomes impossible to fill up only the contact hole with tungsten. By use of this technology, maximum thickness of selective growth is approximately 2000.about.3000 .ANG. (i.e., 0.2.about.0.3 .mu.m) so that it is impossible to completely fill the contact hole whose depth is 0.5.about.1 .mu.m. Therefore, it may occur that junctions are broken down, wiring is broken and reliability decreases.